When I record the microphone input alone, it sounds on both channels. If I record it on stereo mix, it sounds only on the left side.
I want to use stereo mix and get mic input in stereo. How do I do this?
There are several possible solutions which don't involve you going insane :)
1) an adapter device exists with mono mini-plug on one side and stereo mini-plug on the other. Depending on which way you use it you can mix stereo to mono or dupe mono (your mic output) to stereo.
2) With software (Audacity for instance) you can post-process mono into stereo with a simple cut and paste.
Assuming your microphone terminates in an 1/8" mini plug, see how many metal rings there are. Two rings means a mono out, three means it 'should' be stereo out.
If the microphone is supposed to be stereo, but you're only getting signal on one of the two channels, a quick fix is just make sure that you create a new track in your recording program, select mono.